It has been long recognized that the value of agricultural products such as cereal grains and the like are affected by the quality of their inherent constituent components. In particular, cereal grains with desirable protein, oil, starch, fiber, and moisture content and desirable levels of carbohydrates and other constituents can command a premium price. Favorable markets for these grains and their processed commodities have therefore created the need for knowing content and also various other various physical characteristics such as hardness.
To meet market expectations, numerous analyzer systems have been developed using near infrared (NIR) spectroscopy techniques to analyze the percentage concentrations of protein and moisture. Some of these systems target cereal grains in milled form as explained, for example, in U.S. Pat. No. 5,258,825. The value added by milling in some instances decreases the economic gain that is obtained by first sorting, and thus others target the analysis of whole grains, as in U.S. Pat. No. 4,260,262.
NIR spectrophotometric techniques are typically favored because of their speed, requiring typically only thirty to sixty seconds to provide results, as compared with the hours of time which would be needed to separate and analyze constituents using wet chemical and other laboratory methods. NIR spectrophotometric techniques are also favored because they do not destroy the samples analyzed. In a typical analysis of wheat grains, for example, a sample is irradiated serially with selected wavelengths. Next, either the sample's diffuse transmissivity or its diffuse reflectance is measured. Either measurement then lends itself to use in algorithms that are employed to determine the percentage concentration of constituents of a substance.
For example, the analyzer described in U.S. Pat. No. 4,260,262 determines the percentage of oil, water, and protein constituents by using the following equations: EQU oil %=K.sub.0 +K.sub.1 (.DELTA.OD).sub.w +K.sub.2 (.DELTA.OD).sub.o +K.sub.3 (.DELTA.OD).sub.p EQU water %=K.sub.4 +K.sub.5 (.DELTA.OD).sub.w +K.sub.6 (.DELTA.OD).sub.o +K.sub.7 (.DELTA.OD).sub.p EQU protein %=K.sub.8 +K.sub.9 (.DELTA.OD).sub.w +K.sub.10 (.DELTA.OD).sub.o +K.sub.11 (.DELTA.OD).sub.p
where (.DELTA.OD).sub.w represents the change in optical density using a pair of wavelengths sensitive to the percentage moisture content, (.DELTA.OD).sub.o represents the change in optical density using a pair of wavelengths sensitive to the percentage oil content, and (.DELTA.OD).sub.p represents the change in optical density using a pair of wavelengths sensitive to the percentage protein consents. K.sub.0 -K.sub.1 are constants or influence factors.
The change in optical density of any given constituent may thus be found from the following equation: EQU .DELTA.OD=log (Ii/Ir).sub.1 -log(Ii/Ir).sub.2
where (Ii/Ir).sub.1 is the ratio of the intensity of incident light to the intensity of reflected light at one selected wavelength, and (Ii/Ir).sub.2 is the ratio of the intensity of incident light to the intensity of reflected light at a second selected wavelength.
Typically, grain analyzers use selected wavelengths in the range of about 1100 to 2500 nanometers. However, in U.S. Pat. No. 5,258,825, particle size effects of flour were overcome by additionally using a 540 nanometer wavelength.
Analyzers of the prior art typically use a filter wheel or scanning diffraction grating to serially generate the specific wavelengths that are of interest in analyzing grain constituents. Because of moving parts, filter wheels and scanning diffraction gratings are sensitive to vibration and are not reliable in analyzing grain during harvesting. They therefore are not suitable for withstanding the mechanical vibrations generated by a combine or other agricultural harvesting equipment, and therefore have not found use in real-time measurement of grain constituents during harvesting.